The present invention is directed to selective deactivation of specified cylinders of an internal combustion engine with a solenoid activated hydraulic actuator that disables intake and exhaust valve lifters, and more particularly to a model-based method of controlling the actuator based on an estimation of the actuator response time.
It is known that fuel economy improvements may be achieved in multi-cylinder internal combustion engines by deactivating selected cylinders during specified engine operating conditions. For example, General Motors Corporation produced engines for 1980 Cadillac vehicles capable of operation with four, six or eight cylinders, depending on engine speed and load. In mechanizing a cylinder deactivation system in an engine with cam-driven valve lifters, the valve lifters for the intake and exhaust valves of a cylinder capable of being deactivated are equipped with solenoid activated hydraulic actuators that when activated, prevent the valves from opening.
In operation, the valve deactivation hardware is actuated in response to a command to deactivate the respective valves, and the actuation must be completed within a given window of opportunity relative to the respective cylinder combustion cycle. In a typical system, for example, the intake and exhaust valves for a cylinder to be deactivated are locked in a closed state during the combustion/power stroke, and prior to the exhaust stroke. To reliably carry out such a method, the controller must have a reasonably accurate estimation of the dynamic response time of the deactivation hardware. However, it is difficult to accurately calibrate or estimate the dynamic response time since it can vary significantly due to variations in the fluid source pressure, temperature, system voltage, and so on. Accordingly, what is needed is a control method based on a more accurate estimation of the overall response time of cylinder deactivation.
The present invention is directed to an improved control method in which the dynamic response of a solenoid-operated hydraulic actuator for deactivating an engine valve mechanism is characterized using a lumped parameter model of the solenoid, the hydraulic sub-system, and a locking pin mechanism actuated by a control pressure developed by the hydraulic sub-system. In response to a mode change request, constituent delay times associated with the solenoid, the hydraulic sub-system, and the locking pin mechanism are determined and summed to form an estimate of the overall delay time required to complete the requested cylinder deactivation. The solenoid activation is then scheduled based on the estimated delay time and a window of opportunity in the engine cycle for cylinder deactivation.